The invention describes a process for operating a centrifuging unit, which includes a centrifuging container, in particular a centrifuging bowl, for separating the components of a liquid containing components with different specific weights, specifically blood. The centrifuging container contains a separation chamber, an inlet for the liquid to the separation chamber, and an outlet for a separated component from the separation chamber. The inlet and outlet extend through a revolving passage at the upper end of the container. The inlet is connected to an inlet channel which empties in the lower area of the container into a separation chamber. The unit includes a pump device to fill and/or empty the centrifuging container, whereby the liquid to be centrifuged is led to the inlet.
In addition, the invention has to do with a centrifuging unit, with a centrifuging container, in particular a centrifuging bowl, for separating components of a liquid containing components with different specific weights, specifically blood. The centrifuging container contains a separation chamber, an inlet for the liquid to the separation chamber, and an outlet for a separated component from the separation chamber. The inlet and outlet extend through a revolving passage at the upper end of the container. The inlet is connected to an inlet channel which empties in the lower area of the container into a separation chamber. The unit includes a pump device to fill and/or empty the centrifuging container.
It is the custom to use centrifuging units to separate components of a fluid with differing specific weights. Such centrifuging units, particularly centrifuging bowls, are used in separating blood, to separate the blood into its components. After donation, blood is normally broken down into its main components, i.e., blood plasma, low-molecular substances and proteins, and the cellular elements, of which red blood cells make up the major portion.
It is known that blood is centrifuged in batch fashion using a centrifuging bowl having an admission volume of several hundred milliliters. For each centrifuging process, this centrifuging bowl is filled with blood and centrifuged until the blood components with differing weights have formed layers and have separated from each other in the bowl. Thereafter, when the centrifuging unit has stopped, the individual components are removed from the bowl.
Such previously customary centrifuging permits only the overflow (i.e., the components with the smallest specific weight) to be obtained when the bowl rotates, until it is filled with heavy components. Then the bowl is stopped and once at rest the heavy components are removed from the stationary bowl. If these heavy components are needed (red blood cells erythrocytes- as a rule, in blood centrifuging), then this step presents the obtaining of the end product. Stopping the bowl, emptying it and refilling it, in order to separate several liters of blood into its individual components, is time-consuming.
One centrifuging unit with a bowl of the type mentioned initially for centrifuging blood is known from the U.S. Pat. No. 3,145,713. As depicted in the figures of this publication, the bowl in one embodiment shape is a cylindrical or conical container with an outer annular chamber which is formed between the exterior container wall and an inner insert. By means of a revolving passage on the outer side of the centrifuge container, blood is fed in via an inlet, roughly in the container""s rotational axis. From this inlet, a channel leads to the base of the centrifuging container, where the blood, still not separated, is passed into the annular chamber. In the upper part of the annular chamber, provision is made for a connection with an outlet which runs through the revolving passage, by means of which the separated, lighter components are removed. After the annular chamber or separation chamber is filled with the heavy red blood cells separated from the blood, the process of admitting is interrupted, and the rotation of the bowl is stopped. Then the red blood cells are appropriately processed and subjected to deep freezing in the bowl, so that the entire unit with the red blood cells can be stored in deep-freeze fashion. It is necessary to equalize pressure in the centrifuging container between the inlet and outlet. To accomplish this, in the upper area, i.e., in the area where rotation takes place, a connection exists between the inlet area and the outlet area or the separation chamber.
Another centrifuge with a container or a bowl is known from the European Patent No. EP-B1-0 015 288. That text essentially is concerned with the special configuration of the rotating passage in the area of which the inlet and outlet are provided. Also in that bowl, the inlet is run via an inlet channel to the bottom area of the bowl, from which the admitted blood is transferred radially outward via a radial channel into an annular separation chamber. The inlet, placed in the area of the container""s axis, is surrounded by an axial annular chamber, leading from the bottom of the bowl to its upper area, where it is short-circuited, i.e., connected, with the outlet or the separation chamber. This connection also serves to equalize pressure between individual chamber areas of the bowl.
Another procedure for separating blood into its components is published in European Patent Application No. EP-A1-0 014 093. The arrangement for carrying out the procedure includes a centrifuge with a rotating basin. In that basin, viewed in the radial direction, two bag-like containers are placed atop each other. Into one of these containers, the blood, not yet separated, is admitted and filled. Following separation, the rotor is stopped and the second container is filled with a liquid. The influx of the liquid into the second container pushes the first component separated from the blood out of the first container.
As the above description of the state of the art shows, and as was already explained, procedures according to the state of the art are carried out in batch fashion, i.e., in each instance, pre-set quantities of blood are processed which match the maximum container filling volume of the centrifuging rotor. Or, the volume of the rotor is used to collect a separated component such as red blood cells. Then the separation chamber, having been filled with these red blood cells, is emptied. Or, this separated component is frozen directly in the centrifuging bowl and stored. If small amounts that are less than the filling volume of such a centrifuging rotor are separated, a danger exists that after the rotor is stopped, the separated component may be mixed with the other separated components.
From the description above it is evident that for separating large quantities of liquid that exceed the filling volume of the centrifuging container, separation into individual batches is necessary, implying multiple starts and stops of the centrifuge, resulting in a time-consuming procedure.
In not only medical technology, but also in biotechnology areas, since separating suspensions using separator bowls by means of gravity gradients results in only slight gravity gradient differences, the liquids to be separated are subject to loads of multiple thousands of g (1 g is simple ground acceleration). Seen in physics terms, in the interior of the separation bowl, the desired gravitational field is created by its rotation. Thus, a centrifugal force F(Z) acts on each particle in the bowl. This force results from the product of the particle""s density and the centrifugal acceleration b(z).
The product of the radius r and the angular velocity squared make up centrifugal acceleration b(z).
Classical bowls have the outlet configured as passing via two closely situated, static disks, which act like a pump or like a sliced disk (see aforementioned U.S. Pat. No. 3,145,713, column 5, lines 20 to 32). The liquid column that forms during operation grows with increasing filling until it reaches the outer edges of this pump. Liquid that touches the disks is decelerated and spun inward and can thus exit via the outlet.
The radius r of these disks is in the area of 2 cm. Thus, in a previously customary bowl filled with liquid, a cylindrical inner zone is formed, also having a radius r, which always remains filled with air. Between the surface of the liquid column and the bowl""s center of rotation, a pressure difference thus forms which can be computed as P=F/A, with A here being the area.
Working out the formula yields a formula P=D*(2P1*r*n)2. From this the interrelation of rpm, radius and the pressure that results from these is derived, as can be seen in the graph (1).
Most classical bowls are filled by the inlet on the lower end of the bowl""s axis of rotation until for example, the separation chamber is filled with a heavy component such as in blood the red blood cells. If this is the case, then rotation of the bowl is halted, the liquid column collapses and then is drained out through the inlet at the foot of the axis of rotation. Here a possible height difference is overcome only by the pump. The volume drained away in the bowl is equalized through air fed through the outlet (see, for example, German Patent Publication No. 27 45 041, page 15, 2nd paragraph, 1st sentence ff.).
With newer bowls an attempt is made to avoid decelerating the bowl by draining them while they are still rotating. This is described in the U.S. Pat. No. 4,879,031. As can be seen from FIG. 1 of this U.S. Pat. No. 4,879,031, the central inlet 11 is made tight against the central channel 6 via seal 14 and 15. Then a subpressure is applied via inlet 11b. The subpressure to be applied must be considerable, since the liquid must be suctioned from a distance that is produced by the axis of rotation (not shown) and a line running parallel to it through the outer circumferential line of disk 13a and 13b. In physics terms, subpressure is limited to 0 bar, the absolute vacuum, and thus to a subpressure of 1 bar in comparison to normal ambient air. Technically, a subpressure that can be generated with normally used roller or peristalsis pumps terminates at about 200 mbar.
The diagram as per FIG. 6, shows how pressure (in bar) is applied in dependence on the radial distance from the bowl""s rotation axis. From this diagram it is evident that at rpms between 4,000 and 8,000xe2x80x94normal for these separation bowlsxe2x80x94a suction of the first divided layer at the physical boundary is taking place. In no instance is it possible to suction at the above-named rpm liquids from areas of the bowl that are farther out radially. One remedy could be to further lower the rpm. This, however, could lead to dissolution of the separation boundaries, which would be contrary to the sense and purpose of this patent""s bowl. One would achieve the same state as if the bowl had been fully halted. The U.S. Pat. No. 4,859,333 has the same initial conditions as were given above. Here also, suction requires the application of a very high subpressure.
Corresponding to the procedure disclosed in the U.S. Pat. No. 4,859,333 and U.S. Pat. No. 4,879,031, in the first phase of suction, no liquid is required, but rather air, which is located in the center to the degree described above.
Also, it is generally known that cells, particularly red blood cells, are very resistant to pressure. If subpressure is applied, however, they tend toward hemolysis.
The U.S. Pat. No. 5,514,070 shows another option for suctioning liquid from a rotating bowl. As can be seen in the figures, provision is made on the lower end of the inlet 26 for a second pump consisting of two disks with the same radii as disks 30 and 32, which form the classical outlet at the upper end. If the separation chamber is filled with a heavy componentxe2x80x94red blood cells, for example, in the case of bloodxe2x80x94then via outlet 18, a lighter component such as common salt is fed in (column 2, line 66 ff.). By this means, the heavier components are compressed through passage P2. It is not possible to xe2x80x9cback-feedxe2x80x9d a heavier component with a lighter component. Therefore, following the principle of linked pipes, the result at minimum will be a dilution. Also, constant sedimentation takes place in annular chamber P3, which is dependent on the sedimentation coefficient. The sedimentation coefficient 3 is normally given in Svedberg units. The sedimentation coefficient 3 is the quotient from the migration speed of particles in the suspension and centrifugal acceleration. It turns out that the migration speed is directly proportional to centrifugal acceleration. This conflicts with the speed at which light liquids are now passed through outlet 18. It stands in a direct relation to the speed at which heavy cells flow through opening E1 into the annular chamber P3. The relation becomes least through the surface of the outlet cross section to the wall surface of annular chamber P3. On the outer diameter of the chamber, the greatest sedimentation rate contrasts with the least flow velocity, directed toward passage P2. By this means, depending on the sedimentation coefficient, the dilution is more or less pronounced.
The previously described state of the art poses a problem which always arises when quantities of liquids are to be separated that exceed the filling volume of the separation chamber of a centrifuging rotor. It also arises when the filling volume of a separation chamber exceeds that of a separated component. To solve this problem, the present invention provides a process of operating a centrifuging unit. It also provides a centrifuging unit to carry out such a process. Using it, even large quantities of liquids to be separated into at least two components can be broken down without stopping the centrifuge in batch-operation fashion. This also provides a possibility of suctioning out the heaviest components at full operational angular velocity of between ca. 4000 and ca. 6000 rpm. (The operating angular velocity is fundamentally limited at the low end by dissolution of the separation boundaries. At the high end, it is limited by the mechanical loading capacity of the separation bowl.) Suctioning is to be accompanied by the least possible dilution.
In relation to a centrifuging unit of the type initially mentioned, the problem is solved by having the inlet, the feed channel, the separation chamber and the outlet, seen in the direction of flow, become flow paths separated from each other. The pump device, reversing the direction of flow between inlet and outlet, can be switched over to withdraw a separated component via the feed channel and the inlet. The transition between the separation chamber and the outlet is situated closed to the rotational axis, at a distance of at most 10 mm, and preferably 2 to 6 mm away from it.
The process according to the invention makes it possible to remove the separated components and heavy fractions of the centrifuging bowl or centrifuging unit without having to stop the unit from rotating. According to the invention-specific process, a sufficient or pre-set quantity of separated components is concentrated in the centrifuging container. After this has been accomplished, the flow direction that was maintained to feed in the not yet separated liquid (i.e., the flow between the inlet and outlet) is reversed. This is done in order to draw off a separated component via the intake channel, which terminates in defined fashion in an area of the separation chamber. This liquid is then drawn off via the actual inlet, then serving as an outlet, in the area of the centrifuging unit""s rotating passage, and expelled outwards. Via the original outlet, as part of removal of the separated component from the separation chamber, a liquid is fed in, in order to fill up the removed volume. This liquid can be a liquid of a type specific to that liquid that was separated. In other words, the new liquid, not yet separated, can be refilled via the outlet, simultaneous with removal of the separated component. Preferably, if blood is being separated, plasma or some other light liquid, such as a common salt solution, should be injected. The separated component is fully withdrawn from the separation chamber. After this is complete, the actual inlet, previously used to remove the separated component, now is employed again to continuously feed in liquid to be separated. This is done until the separation chamber is again occupied by components from the liquid to be separated. Thereafter, the direction of flow, as mentioned above, is reversed again, so that separated components can again be removed. So that the process according to the invention can be implemented in regard to the centrifuging unit, it is essential that the flow paths between the inlet, the intake channel, the separation chamber and the outlet be flow paths that are separated from each other. In other words, only a specified flow of liquid is possible from area to area. Such a centrifuging unit may not have any direct flow connections between inlet and outlet, for example to do any pressure compensations. Otherwise, when flow directions are reversed between feed-in and removal of a separated component, such short-circuit links could permit re-filled liquid for filling the removed volume to flow directly to the outlet and mix with the separated component. Preferably, such a procedure and such a centrifuging unit according to the invention will cause a separated component with a high specific gravity to be removed from the centrifuge. However, it is also possible to have lighter components that are separated from a liquid such as blood to be removed from the separation chamber using the invention-specific procedure. For this, the centrifuging container must have an appropriate shape relative to the centrifuging unit""s rotation axis. The feed channel, via which the separated component is to be withdrawn, must terminate in a zone in which the separated component of the fluid to be removed is collected.
The objective is to suction out components from the fluid which possess a high specific weight. To accomplish this, a preferred procedure and a preferred centrifuging unit configuration call for the feed channel to terminate in the bottom area of the centrifuging container. Then the centrifuging unit can be operated long enough to permit essentially the entire separation chamber to be occupied by the specific heavy liquid component which is continuously fed via the feed channel. Meanwhile, the lighter components are expelled via the outlet channel. Only after a sufficient quantity has been collected is the direction of flow again reversed, to feed in the heavy components, while the centrifuging container continues to be rotated. The centrifuging unit is constantly rotating, even during removal of separated components. It will be evident, therefore, that no components get mixed with other components having a different specific weight which are not to be withdrawn immediately.
The following structural details and properties are significant:
Even at full operation rpm, the bowl or centrifuging container is to be completely filled with liquid. The opening of the outlet must begin directly at the wall of the inlet. No pressure differences can then form in a separating bowl completely filled with liquid.
Additionally, inlet channels should be provided whose openings empty as wide as possible on the lower diameter in the separation chamber. These inlet channels should have the smallest possible diameter (ca. 2 to 6 mm, to achieve a high flow velocity during suctioning.
Procedural care is to be taken that the bowl is always filled with liquid, as long as withdrawal at high operational rpm is desired. This means that the liquids or suspension drained out through the opening of the inlet channel and the outlet must simultaneously be replaced by a suitable liquid or suspension via the other inlet or outlet. This ensures that the system will be pressure-free.
When filling commences, the still empty bowl must not be turning at all, or else very slowly. This will have the effect of attaining a complete filling of intake channels. The eddying effect in a centrifugal pump that arises when the bowl is not completely filled will be minimized. However, it may be desired to intentionally induce this effect, for example to suction liquids to be separated out of the vessels, or compensate for pressure losses in the hose systems. This is done by a calculated adaptation of rpm to the desired suction effect.
If the bowl is filled completely or almost completely, the desired operating rpm can be attained. The suspension is divided in according to with the various densities. In blood, for example, the plasma will collect toward the center, while heavier red blood cells move outward. Between these two fractions, the white blood cells and thrombocytes collect as a thin layer.
If blood continues to fill in, the plasma is withdrawn through an overflow channel and the outlet. The bowl can be filled if desired mechanically by devices such as a pump. Or, filling can be done by gravity, by means such as directly via a needle with a suitable hose from a dispenser positioned somewhat higher than the separating bowl.
To automate the procedure, a sensor device is planned, which would detect a certain filling level in the centrifuging container of the component to be separated and then removed. It then issues a pulse which controls the pump device by reversing direction. Preferably, this is an optical device which, in addition, is positioned outside the centrifuging container, and thus does not rotate with it. The pump device initially has fed in liquid to be separated via the inlet. After the above-mentioned full level impulse is emitted, the pump device reverses its direction, to remove the separated component to the centrifuging container via the attachment that normally serves as an inlet. The volume of the separation chamber is a known quantity. Therefore, the amount to be withdrawn, i.e., the amount of the separated component, can be pre-adjusted. This is done so that after the removal of a pre-set, defined volume of separated component, the pump device can again reverse its pumping direction, and again admit liquid to be separated via the inlet.
The intake channel of the centrifuging unit according to the invention is preferably divided into two chambers, with the first section running with its axis along the rotational axis of the centrifuging container. This axis constitutes the neutral zone of the centrifuging unit. For one thing, this arrangement ensures that separation of the not yet separated liquid takes place in the neutral zone, not in the inlet channel; for another, the center of the centrifuging unit""s gravity remains by this means on the rotational axis. The second section of the inlet channel can then be in two parts. In other words, on the end of the first section, the second section on opposite sides can be made to branch out radially. If more than two channels are provided, care should always be taken to maintain a certain symmetry, so that the rotation of the centrifuging unit results in no unbalancing. Should only a single feed channel, or a single second section for the feed channel be provided, the radially opposite side should be appropriately weight-balanced. A single feed channel is advantageous in that it is exactly during suctioned withdrawal that a relatively small suctioning cross section is provided. This makes it possible to withdraw as much of the separated component as possible, without collecting additional components.
The aim is to use the volume of the centrifuging container as much as possible for separation. To achieve this, the container is configured so that the separation chamber and the feed channel are separated from each other by a common dividing wall. This means that no additional intermediate space exists between the the feed channel and the separation chamber. The feed channel is designed with a relatively small diameter, in the neighborhood of a few millimeters. However, the overall radial area that surrounds the feed channel, out to the exterior side of the container, is used for the separation chamber. Depending on the components to be separated, the separation chamber is to have a specific shape and orientation to the rotational axis. Preferred is a configuration in which the separation chamber, in its extension in the flow direction to the rotational axis, runs at an incline. This is so that the end toward the outlet is closer to the rotational axis than the passage between the feed channel and the separation chamber. The outlet channel is that channel via which, during operation to separate components, those components are withdrawn which do not remain as separated components in the separation chamber during the separation phase.
Further particulars and features of the invention can be gleaned from the following description of embodiment examples with reference to the drawings.